Soft brakes
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 801
Likes: 17
From: Middletown Delaware
Soft brakes
OK I have read all the post I could find on soft brakes but none talk about the light coming on also. This 77 vette has all new brake lines and on its second master cylinder for this problem and pedal is still soft. MC was bench bled and system was pressure bled but the more I read I think my sequence is incorrect I used. RR LR RF LF As i said I do get the brake light when pedal goes to floor. Do you think a rebleed is the answer or other problem . Dave
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
OK I have read all the post I could find on soft brakes but none talk about the light coming on also. This 77 vette has all new brake lines and on its second master cylinder for this problem and pedal is still soft. MC was bench bled and system was pressure bled but the more I read I think my sequence is incorrect I used. RR LR RF LF As i said I do get the brake light when pedal goes to floor. Do you think a rebleed is the answer or other problem . Dave
Be sure to check to see if you have 2 bleeders on each caliper (top only of each "half") and bleed from both if you do.
Last edited by pws69; Mar 19, 2008 at 01:04 PM.
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
Yes, it sounds like air is the culprit. As far as the bleeding sequence, it is the opposite of what you are doing. You should start with the caliper closest to the MC with the furtherest, RR, being the last. This is according the the GM shop manual. However, I don't think sequence is that inportant. 
Melting Slicks
Joined: Dec 2006
Posts: 2,669
Likes: 3
From: Kingston Ontario
GM sequence, for a '77 is as follows;
left rear
right rear
left front
right front
Combination/Proportioning valve causes the dash light to illuminate when low pressure is sensed on either the front or rear system. (An internal piston shifts left or right to activate the switch.)
I would pressure bleed following the above sequence. Lightly tap each caliper with a rubber hammer while bleeding, to dislodge any stuck air bubbles. Following the system bleed apply a very hard brake application to reset the combination/proportioning valve. (This hard brake application puts high pressure on both sides of the internal piston to re-centre it.)
Test system again for brake pedal feel and re-bleed if necessary.
left rear
right rear
left front
right front
Combination/Proportioning valve causes the dash light to illuminate when low pressure is sensed on either the front or rear system. (An internal piston shifts left or right to activate the switch.)
I would pressure bleed following the above sequence. Lightly tap each caliper with a rubber hammer while bleeding, to dislodge any stuck air bubbles. Following the system bleed apply a very hard brake application to reset the combination/proportioning valve. (This hard brake application puts high pressure on both sides of the internal piston to re-centre it.)
Test system again for brake pedal feel and re-bleed if necessary.
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 801
Likes: 17
From: Middletown Delaware
WOW what a difference the correct sequence made. I even saw a big shot of air come out after a couple ounces on the RR. I rebled a 76 I have also that has decent brakes and there was a also a big improvement and a bid shot of air after bleeding awhile. MY guess is bleeding the worng sequence is traping air in system. Thanks Dave 
Instructor
Joined: Jul 2007
Posts: 213
Likes: 0
From: Nowhere Mars (Southern Indiana)
WOW what a difference the correct sequence made. I even saw a big shot of air come out after a couple ounces on the RR. I rebled a 76 I have also that has decent brakes and there was a also a big improvement and a bid shot of air after bleeding awhile. MY guess is bleeding the worng sequence is traping air in system. Thanks Dave
